1. The Field of the Invention
The present invention relates to infrared illuminant compositions. More particularly, the present invention is related to infrared illuminating compositions which produce specific illumination in the spectral region observed with infrared image intensifiers with minimal visible light production.
2. Technical Background
Infrared illuminant flares are used to enhance the use of infrared image intensifiers such as night vision goggles. These flares are generally configured in much the same manner as visible light emitting flares. Thus, these flares may provide infrared radiation at a single position on the ground or they may be propelled over the area of interest and ignited to provide radiation above the ground. Generally, it is desirable that such flares radiate predominantly or almost exclusively in the infrared region and produce little or substantially no visible light. It will be appreciated that it is often desirable to conduct operations in a covert manner which avoids illuminating the observer and does not alert the target, or others, to the presence of the flare.
Infrared illuminant compositions and flares have been developed but problems exist. Among the problems encountered is the presence of undesired visible light during burning. In that regard, the performance of infrared emitting devices can be judged by the ratio of infrared light to visible light observed during combustion. This ratio is known as the concealment, or covert, index. The concealment index is low for many conventional infrared emitting compositions, indicating a high proportion of visible light being emitted from the flare.
The alkali metals potassium, cesium, and rubidium are known to generate infrared radiation upon burning. Nitrates of these metals produce low levels of visible light. Thus, known infrared illuminating compositions with good concealment indexes generally comprise one or more of these metal nitrates. Cesium and rubidium exhibit substantially similar properties and are considered generally interchangeable. Some problems encountered include the relative expense of cesium and rubidium compounds and the relatively slower burn rate and lesser infrared efficiency of potassium nitrate. The combination of cesium and potassium nitrate, however, yields cost-effective compositions with satisfactory burn rates, improved infrared efficiency, and low concealment indexes.
Although compositions comprising a combination of cesium nitrate and potassium nitrate have low concealment indexes, the significant relative contribution of the potassium ion to the visible light produced has not been previously recognized. In addition, these compositions produce some black body radiation in the visible range because the volatile metal combustion products increase the burning temperature of the composition. These problems have not been previously addressed in the art.
Ammonium nitrate is an inexpensive and well-known oxidizing material which has been used effectively in various explosives and propellants. Although ammonium nitrate has been suggested for use in conventional illuminating flares, it has been shown to lack effectiveness in these compositions. Ammonium nitrate produces neither infrared nor visible light when burned. Ammonium nitrate has not been used in conventional infrared illuminating flares.
In summary, known infrared emitting compositions have been found to be less than ideal. State of the art compositions combine potassium nitrate and cesium nitrate. The detrimental contribution of potassium to the flame of these compositions, however, has not been previously recognized. In fact, potassium both produces visible light during its combustion and contributes volatile combustion products which increase the visible signature produced by black body radiance.
It would, therefore, be a significant advancement in the art to provide infrared emitting compositions which produce only minimal visible light while providing specific illumination in the spectral range visible with night vision devices. The compositions would provide high levels of infrared emissions yet avoid the visible light contribution due to the presence of potassium in conventional compositions. The compositions provided, therefore, would have improved concealment indexes.
Such compositions are disclosed and claimed herein.